1. Field
The disclosure relates to a ventilation system, more particularly to a ventilation apparatus employing a swirler fan formed with plural fins on an annular disk with the opening at the center portion to improve efficiency.
2. Description of Related Art
Air moves from high atmospheric pressure region to low atmospheric pressure region. The mechanical fans are utilizing this aerodynamic principle. Rotating blades pushes air outwards and thereby the atmospheric pressures around the blades are lowered. Then air in surroundings in relatively high atmospheric pressure moves toward the blades. By the directions of blades' distortion, air is suctioned or discharged.
A ventilation fan is used to eliminate contaminants (gases, dusts or particles) in a certain space. A range hood for kitchen made of a ventilation fan is used to discharge pollutants and food odors generated during cooking to the outside by driving a fan so as to prevent them to be dispersed to other space. And a portable dust collector or a portable welding fume extractor made of a ventilation fan is used to eliminate dusts, oil mist, fume, etc. generated in local work places.
In general, a ventilation fan is configured to install pipes in the walls or on the ceilings and to dispose an exhaust vent to the outside, and further, to install an exhaust fan adjacent to an exhaust vent, disposed at the front side of the pipe or the rear side of the pipe. Here, a centrifugal fan (a sirocco fan or a turbo fan) is most commonly used for the exhaust fan to be installed, and infrequently, an axial propeller fan is used.
A ventilation fan is based on the assumption that a fan generates the negative pressures and makes airflow movements toward an exhaust inlet, then contaminants in the space will be carried out with the air exhausted. However, to carry out contaminants to the exhaust in the presence of distributing side flows, gravitational settling, and inertial breakaways of contaminants themselves, the fan has to generate high enough air velocity at the position in which contaminants exist. It is the capture velocity. The minimum capture velocity in quiet air is 50 fpm (0.25 m/s) according to “ACGIH Industrial ventilation: A manual of recommended Practice, 23rd edition”. It means that in case the air velocity generated by a ventilation fan is lower than the minimum capture velocity, the contaminants can't be carried out with the air but just light air are exhausted.
Such a ventilation fan of the related art is disadvantageous in that the capture region of contaminants is only defined at the part adjacent to an inlet as illustrated in the diagram of simulation of FIG. 1. That is, when using the exhaust fan configured in a manner such that a plurality of projected blades are arranged at a predetermined interval on a cylindrical body, the air velocity suctioned rapidly decreases inversely proportional to the square of a distance from the entrance of the exhaust vent. Due to such a property, the suction power rapidly drops unless the exhaust fan is installed to be adjacent to a source to generate contaminants.
As illustrated in FIG. 2 (velocity Contours—plain circular opening—% of opening velocity; American Conference of Governmental Industrial Hygienists (ACGIH): Industrial Ventilation Manual, 23rd Edition), this is because that, although the rotation of a typical exhaust fan generates an ascending air current, the velocity of the air current at a position dropped as much as the diameter of the entrance of the exhaust vent is reduced to about 7.4% of the air velocity at the entrance of the exhaust vent.
Such a phenomenon that the velocity is reduced inversely proportional to the square of a distance from the entrance of the exhaust vent is well-known as Dalle Valle equation. Dalla Valle Equation is,
  Vx  =      Vf                  12.7        ×                              (                          x              d                        )                    2                    +      0.75      Where Vx is velocity at x
Vf is a face velocity at the exhaust inlet                x is a distance from the exhaust inlet        
d is a diameter of exhaust inlet.
For the velocity x=1d
      Vx    =                  Vf                              12.7            ×                                          (                                  1                  1                                )                            2                                +          0.75                    =                        Vf          13.45                =                  0.074          ⁢                                          ⁢          Vf                      ,Consequently, the velocity at x=1d, decreases to 7.4% of the face velocity at the exhaust inlet.
Regardless of such a mechanism, in the configuration of the ventilation fan, the exhaust vent is positioned at a point away from the contaminant's source farther than the diameter of the entrance of the exhaust vent so that the discharge power thereof is extremely low. Accordingly, all the existing exhaust apparatuses including a range hood attempt to increase the discharge power by increasing exhaust air volume to raise the air velocity.
However, according to Fan Affinity Law, in order to double the air velocity, it is necessary to increase the power consumption of a fan by 23, that is, eight times (cubic law of air velocity), which is problematic because the power consumption becomes too great and accordingly, the noise thus caused increases.
Power consumption of centrifugal fan by Fan Affinity Law is,P1/P2=(n1/n2)3(d1/d2)5,q1/q2=(n1/n2)(d1/d2)3 
where
P=power (W, bhp, . . . )
q=volume flow capacity (m3/s, gpm, cfm, . . . )
n=wheel velocity—revolution per minute—(rpm)
d=wheel diameter